Optoelectronic devices are becoming increasingly important to a number of industries such as, for example, the telecommunication industry. Exemplary optoelectronic-based devices include laser diods (LD), light emitting diodes (LEDs), and photodetectors (PDs). These devices are fabricated with an optically active region made of semiconducting materials that have different lattice constants than the substrate on which they are located. Silicon (Si) is a well known substrate material used in integrated circuit technologies and has developed a mature technological base with respect to its use in fabricating integrated circuits. Unfortunately, silicon is unable to emit light and therefore cannot be used in the “active” portion of optoelectronic devices for the emission or detection of optical radiation.
There have been unsuccessful efforts in the past to integrate compound semiconductor materials that are optically active (e.g., they emit optical radiation) with silicon. The primary obstacle in integrating compound semiconductor materials in silicon are the crystalline defects produced caused by the growth of the compound semiconductor materials on the silicon substrate. The defects are the result of the relatively large lattice mismatch (i.e., different lattice constants) between the adjacent compound semiconductor materials and the underlying silicon substrate. For instance, there is an approximately 11% lattice mismatch between InAs and Si, and a 4% lattice mismatch between GaAs and Si. InGaAs is an alloy of two compound semiconducting material (InAs and GaAs) that emits light at a wavelength ranging from 0.8 μm to above 1.5 μm—the wavelength for most of the optical fiber network that serves current telecommunication needs (e.g., the internet and other WANs).
InGaAs, when epitaxially grown on Si <001> substrates, is known to have a critical layer thickness on the order of 10 angstroms. Thus, the thickness of InGaAs which can be grown epitaxially on a Si substrate is below 10 angstroms. In comparison, the thickness of a typical quantum well laser formed from InGaAs is on the order of 2000 angstroms. Consequently, dislocation in InGaAs has been unavoidable. Dislocation introduced by epitaxial film relaxation severely limits the performance and useful life of optoelectronic devices including, for example, semiconductor lasers.
There thus is a need for a device and method in which compound semiconductor materials are employed on silicon substrates. Preferably, the device can be created by epitaxially forming the optically active region of optoelectronic devices on a silicon substrate. Preferably, the device may be formed with a very small or limited amount of optically active material.